// Copyright (c) 2000 Just Objects B.V. <just@justobjects.nl>
// Distributable under LGPL license. See terms of license at gnu.org.

package nl.justobjects.pushlet.core;

/**
 * Abstract Event source from which Events are pulled.
 *
 * @version $Id: EventPullSource.java,v 1.4 2003/08/15 08:37:40 justb Exp $
 * @author Just van den Broecke - Just Objects &copy;
 **/

/** ABC for specifc EventPullSources. */
abstract public class EventPullSource implements EventSource, Runnable {
	private volatile boolean alive = false;
	private volatile boolean active = false;
	private static int threadNum = 0;

	public EventPullSource() {
	}

	abstract protected long getSleepTime();

	abstract protected Event pullEvent();

	public void start() {
		Thread t = new Thread(this, "EventGenerator" + (++threadNum));
		t.setDaemon(true);
		t.start();
	}

	public boolean isAlive() {
		return alive;
	}

	/** Stop the event generator thread. */
	public void kill() {
		alive = false;
	}

	/** Activate the event generator thread. */
	synchronized public void activate() {
		if (active) return;
		active = true;
		if (!alive) {
			start();
			return;
		}
		Log.debug(getClass().getName() + ": notifying...");
		notifyAll();
	}

	/** Deactivate the event generator thread. */
	public void passivate() {
		if (!active) {
			return;
		}
		active = false;
	}

	/** Main loop: sleep, generate event and publish. */
	public void run() {
		Log.debug(getClass().getName() + ": starting...");
		alive = true;
		while (alive) {
			try {

				Thread.sleep(getSleepTime());

				// If passivated wait until we get
				// get notify()-ied. If there are no subscribers
				// it wasts CPU to remain producing events...
				synchronized (this) {
					while (!active) {
						Log.debug(getClass().getName() + ": waiting...");
						wait();
					}
				}

			}
			catch (InterruptedException e) {
			}

			// Derived class should produce an event.
			Event event = pullEvent();

			// Let the publisher push it to subscribers.
			Publisher.getInstance().publish(event);
		}
	}
}

/*
  * $Log: EventPullSource.java,v $
  * Revision 1.4  2003/08/15 08:37:40  justb
  * fix/add Copyright+LGPL file headers and footers
  *
  * Revision 1.3  2003/08/12 09:57:05  justb
  * replaced all print statements to Log.*() calls
  *
  * Revision 1.2  2003/05/18 16:15:08  justb
  * support for XML encoded Events
  *
  * Revision 1.1.1.1  2002/09/24 21:02:31  justb
  * import to sourceforge
  *
  * Revision 1.1.1.1  2002/09/20 22:48:17  justb
  * import to SF
  *
  * Revision 1.1.1.1  2002/09/20 14:19:03  justb
  * first import into SF
  *
  * Revision 1.3  2002/04/15 20:42:41  just
  * reformatting and renaming GuardedQueue to BlockingQueue
  *
  * Revision 1.2  2000/08/21 20:48:29  just
  * added CVS log and id tags plus copyrights
  *
  *
  */
